Merc 260 offshore issue diagnoses

[ONE-A-DAY]

I just finished up the change over form carb'd 2.4's to EFI 260 2.5's. One motor runs like a raped ape, the other not as raped. It runs, but is down on power, difficult to start, and smokes much more than the other, plugs are pretty wet.

Since I have two motors I have been swapping around parts in hopes of trying to pinpoint the issues. I swapped the ECU's, made no difference, the great motor ran great still, the poor motor still ran poor. I also swapped the fuel injection harnesses as well, made no difference.

The injectors in both motors have been removed, cleaned and bench flowed and they all check out. Fuel pressure in both motors is at spec in both engines from the Bosch pumps.

Every wire connection, ground etc., has been double checked.

So I am thinking my next test would be to swap the coil packs and see if that corrects the issue in the poor running one.

Thoughts?

[powerabout]

leak down test/comp test on both

[ONE-A-DAY]

leak down test/comp test on both

Done already, 130 ish in all 12 cylinders, and leak down is less than 10% in all.

[outasite]

Try swapping the fuel regulators.Even though static pressure is ok, they can do some weird things.

[Dave Strong]

Also try swapping the intake air temp sensors.

Dave

[phantom16ft]

swapping coils would be an easy one to try and eliminate them as an issue, if that or any of the above doesn't work try swapping switchboxes (make sure to do it in pairs), I've also had intermittent issues with rectifiers killing power. If no joy then its on to stator and trigger. At least you have one working engine to prove out parts.

[STV_Keith]

Make sure the nipple in the horn where the ECU hose gets plugged in isn't plugged/blocked. If it were, the ECU would see no vacuum and give WOT fuel all the time. If you have a scan tool or have access to one (Joe ), look at MAP and see what it reads.

[johnmiffco]

as stated 1st place to go is the vacuum fitting at the horn
they plug up with oil goo all the time and motor goes fat and lazy,,,,,

[patchesII]

Check the barb fitting like they describe. If that doesn't work swap the injectors. I know you said they were bench tested but I've chased my tail over a set of injectors. Other thing would be switch boxes. You didn't say exactly what was wrong with how it ran, just it ran poorly??

[mn808gade]

ck gearcase for tuner pieces/exh blockage?-th

[ChrisCarsonMarine]

Have you looked at the reeds...

[blowitup]

Start it,use timing light and check each cylinder for spark or erratic spark.

[WillySteve]

Also try swapping the intake air temp sensors.

Dave

AND check the Stator voltages then Switch Boxes next!

[A164]

What was the end of this story?
I have also a Merc 260, which is running rough when it is in gear and ideling under 1500rpm. I have changed almost everything, beside the injectors. And and I have rigged up a way to make a flow test, where i found som issues. Mine has reasonable alike flow when the pulse is quite long 4,25 millisec. Then the flow goes wrong when i make the pulses shorter. So I would like to know if have found something similar, og yours was different problem?

[WillySteve]

Never heard, but a stopped up barbed fitting OR the air temp sensor are prolly the 2 main reasons for rich mixture rough idle. Neither will cause it to be down on wot power though.